Device and method for controlling internal combustion engine

ABSTRACT

An internal combustion engine ( 1 ) generates power by burning a mixture of fuel and air in each combustion chamber  3 . The internal combustion engine  1  is provided with an in-cylinder pressure sensor ( 15 ) disposed in each combustion chamber ( 3 ) and an ECU ( 20 ). The ECU ( 20 ) calculates control parameters at two predetermined points, each of which is a product of an in-cylinder pressure detected by the in-cylinder pressure sensor ( 15 ) and a value obtained by exponentiating an in-cylinder volume at the timing of detecting the in-cylinder pressure with predetermined index, as well as calculates a correction value of a fuel injection quantity based upon a difference in the control parameter between the two predetermined points. One of the two predetermined points is set after an intake valve (Vi) opens and before an ignition plug ( 7 ) ignites, and the other is set after the ignition plug ( 7 ) ignites and before an exhaust valve (Ve) opens.

TECHNICAL FIELD

The present invention relates to a control apparatus and a controlmethod for an internal combustion engine which generates power byburning a mixture of fuel and air in a cylinder.

BACKGROUND ART

Conventionally, Patent Document 1 discloses a control apparatus for aninternal combustion engine which is provided with an in-cylinderpressure sensor disposed in each cylinder and calculating means forcalculating heat production for every unit crank angle per each cylinderduring combustion stroke based upon a pressure signal from eachin-cylinder pressure sensor. In this control apparatus for the internalcombustion engine, a fuel supply quantity (air-fuel ratio in eachcylinder) to each cylinder is corrected based upon a calculation resultof the calculating means in such a way that the heat production in eachcylinder becomes the same level with each other. In addition, PatentDocument 2 and Patent Document 3 disclose a control apparatus for aninternal combustion engine which determines a changing quantity ofin-cylinder pressures between minute crank angles sampled by in-cylinderpressure detecting means as a heat generation rate and then, corrects afuel supply quantity or an exhaust gas-recirculating quantity to anintake system based upon the determined heat generation rate during ahigh-load operational region. Further, Patent Document 4 discloses amethod which controls ignition timing, an air-fuel ratio, an exhaustgas-rescirculating quantity and fuel injection timing by using a valueobtained by subtracting a pressure integral value before a top deadcenter from a pressure integral value after a top dead center, eachpressure integral value being calculated by integrating the in-cylinderpressures.

The above-mentioned conventional control apparatus for the internalcombustion engine basically performs integral processing or differentialprocessing of the in-cylinder pressures detected by the in-cylinderpressure detecting means for every minute crank angle. As a result, thecalculating loads in the conventional control apparatus becomeremarkably large and therefore, it is practically difficult to apply theconventional control apparatus to an internal combustion engine for avehicle, for example.

[Patent Document 1] Japanese Patent Application Laid-Open No. 63-268951

[Patent Document 2] Japanese Patent Application Laid-Open No. 4-81534

[Patent Document 3] Japanese Patent Application Laid-Open No. 4-81557

[Patent Document 4] Japanese Patent Application Laid-Open No.2001-152952

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide a control apparatusand a control method for an internal combustion engine with practicalitywhich is capable of simply carrying out high-accurate engine control atlow loads.

A control apparatus for an internal combustion engine according to thepresent invention is characterized in that a control apparatus for aninternal combustion engine which generates power by burning a mixture offuel and air in a cylinder thereof comprises in-cylinder pressuredetecting means for detecting an in-cylinder pressure, calculating meansfor calculating a control parameter based upon the in-cylinder pressuredetected by the in-cylinder pressure detecting means and an in-cylindervolume at a timing of detecting the in-cylinder pressure, and controlmeans for setting a predetermined control quantity based upon thecontrol parameter calculated by the calculating means.

It is preferable that the control parameter includes a product of thein-cylinder pressure detected by the in-cylinder pressure detectingmeans and a value obtained by exponentiating the in-cylinder volume atthe timing of detecting the in-cylinder pressure with a predeterminedindex.

It is preferable that the calculating means calculates the controlparameters at two predetermined points, and the control means sets apredetermined control quantity based upon a difference in controlparameter between the two predetermined points.

It is preferable that one of the two predetermined points is set as apoint after the opening of an intake valve and before the combustionstarting of the mixture and the other is set as a point after thecombustion starting and before the opening of an exhaust valve.

It is preferable that the control means determines a deviation betweenthe difference in the control parameter calculated previously and thedifference in the control parameter calculated at this time on apredetermined condition, and sets a control quantity for correcting anair-fuel ratio of the mixture based upon the determined deviation.

It is preferable that the control means sets a control quantity forcorrecting an air-fuel ratio of the mixture so that the difference inthe control parameter is equal to a target value on a predeterminedcondition.

A control method for an internal combustion engine according to thepresent invention is characterized in that a control method for aninternal combustion engine which generates power by burning a mixture offuel and air comprises the steps of:

(a) detecting an in-cylinder pressure;

(b) calculating a control parameter based upon the in-cylinder pressuredetected in the step (a) and an in-cylinder volume at a timing ofdetecting the in-cylinder pressure; and

(c) setting a predetermined control quantity based upon the controlparameter calculated in the step (b).

It is preferable that the control parameter includes a product of thein-cylinder pressure detected in the step (a) and a value obtained byexponentiating the in-cylinder volume at the timing of detecting thein-cylinder pressure with a predetermined index.

It is preferable that in the step (b), the control parameters arecalculated at two predetermined points and in the step (c), apredetermined control quantity is set based upon a difference in thecontrol parameter between the two predetermined points.

It is preferable that one of the two predetermined points is set as apoint after the opening of an intake valve and before the combustionstarting of the mixture and the other is set as a point after thecombustion starting and before the opening of an exhaust valve.

It is preferable that the step (c) includes the step of determining adeviation between the difference in the control parameter calculatedpreviously and the difference in the control parameter calculated atthis time on a predetermined condition and the step of setting a controlquantity for correcting an air-fuel ratio of the mixture based upon thedetermined deviation.

The step (c) may include the step of setting a control quantity forcorrecting an air-fuel ratio of the mixture so that the difference inthe control parameter is equal to a target value on a predeterminedcondition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing a correlation between a control parameterPV^(κ) used in the present invention and heat production in a combustionchamber;

FIG. 2 is a graph showing a correlation between an air-fuel ratio of amixture in a combustion chamber and heat production between twopredetermined points;

FIG. 3 is a schematic construction view of an internal combustion engineaccording to the present invention; and

FIG. 4 is a flow chart for explaining operations of the internalcombustion engine in FIG. 3.

BEST MODE FOR CARRYING OUT THE INVENTION

The inventors have devoted themselves to the study for enabling anaccurate control in an internal combustion engine with reduction ofcalculation loads thereon. The inventors has resulted in recognizing acontrol parameter calculated based upon an in-cylinder pressure detectedby in-cylinder pressure detecting means and an in-cylinder volume at thetiming of detecting the in-cylinder pressure. In more detail, when anin-cylinder pressure detected by in-cylinder pressure detecting means ata crank angle of θ is set as P (θ), an in-cylinder volume at a crankangle of θ is set as V (θ) and a ratio of specific heat is set as κ, theinventors have focused attention on a control parameter P (θ)·V^(κ) (θ)(hereinafter referred to as PV^(κ) properly) obtained as a product of anin-cylinder pressure P(θ) and a value V^(κ) (θ) determined byexponentiating the in-cylinder pressure (θ) with a ratio κ of specificheat (a predetermined index). In addition, the inventors have found outthat there is a correlation, as shown in FIG. 1, between a changingpattern of heat production Q in a cylinder for an internal combustionengine to a crank angle and a changing pattern of a control parameterPV^(κ) to a crank angle. It should be noted that in FIG. 1, −360°, 0°and 360° respectively correspond to a top dead center, and −180° and180° respectively correspond to a bottom dead center.

In FIG. 1, a solid line is produced by plotting control parametersPV^(κ) each of which is a product of an in-cylinder pressure in a modelcylinder detected for every predetermined minute crank angle and a valueobtained by exponentiating an in-cylinder volume at the timing ofdetecting the in-cylinder pressure with a predetermined ratio κ ofspecific heat. In addition, in FIG. 1, a dotted line is produced bycalculating and plotting heat production Q in the model cylinder basedupon the following formula (1) as Q=∫dQ. It should be noted that in anycase, κ=1.32 for simplification. $\begin{matrix}\lbrack {{Number}\quad 1} \rbrack & \quad \\{\frac{\mathbb{d}Q}{\mathbb{d}\theta} = {\{ {{\frac{\mathbb{d}P}{\mathbb{d}\theta}V} + {k \cdot P \cdot \frac{\mathbb{d}V}{\mathbb{d}\theta}}} \} \cdot \frac{1}{k - 1}}} & (1)\end{matrix}$

As seen from the result shown in FIG. 1, a changing pattern of heatproduction Q to a crank angle is generally identical (similarity) to achanging pattern of a control pattern PV^(κ) to a crank angle and inparticular, it is found out that, after and before the combustionstarting (at the spark igniting time in a gasoline engine and at thecompression igniting time in a diesel engine) of a mixture in a cylinder(for example, the range of from about −180° to about 135° in FIG. 1),the changing pattern of the heat production Q is extremely identical tothe changing pattern of the control parameter PV^(κ). Accordingly, whena predetermined control quantity is set based upon a control parameterPV^(κ) calculated based upon an in-cylinder pressure detected by thein-cylinder pressure detecting means and an in-cylinder volume whendetecting the in-cylinder pressure by using a correlation between heatproduction Q and a control parameter PV^(κ) found out by the inventors,an engine control with high accuracy and good response reflecting heatproduction Q in a cylinder can be simply performed without requiringcalculation processing with high loads.

In this way, in a control apparatus for an internal combustion engineaccording to the present invention, on a basis of the new realization asdescribed above, a predetermined control quantity is set based upon acontrol parameter calculated based upon an in-cylinder pressure detectedby in-cylinder pressure detecting means for detecting the in-cylinderpressure and an in-cylinder volume at the timing of detecting thein-cylinder pressure, i.e. based upon a control parameter (PV^(κ)),which is a product of an in-cylinder pressure detected by thein-cylinder pressure detecting means and a value obtained byexponentiating an in-cylinder volume at the timing of detecting thein-cylinder pressure with a predetermined index. It should be noted thatin the present invention, “the setting of a control quantity” includescalculating a control quantity of an air-fuel ratio of a mixture itselfor the like and also setting (calculating) a control quantity forcorrecting the air-fuel ratio of the mixture or the like.

In addition, it is preferable that the control parameters are calculatedat two predetermined points and a predetermined control quantity iscalculated based upon a difference in the control parameter between thetwo predetermined points.

As described above, the control parameter PV^(κ) on which the inventorshave focused attention reflects heat production Q in a cylinder for aninternal combustion engine and a difference in the control parameterPV^(κ) between two predetermined points (for example, two points afterand before combustion starting in a cylinder (at the spark ignited timeor the compression ignited time)) shows heat production ∫dQ in acylinder between the two points (a value obtained by integrating dQ, forexample, in the range of θ1 to θ2 (θ1<θ2), the same hereinafter) and canbe calculated at extremely low loads. Accordingly, it is possible toaccurately set a predetermined control quantity in accordance with heatproduction in a cylinder with the calculation loads reduced by a largeamount by using a difference in the control parameter between twopredetermined points. In this case, it is preferable that one of the twopredetermined points is set as a point after the opening of an intakevalve and before the combustion starting and the other is set as a pointafter the combustion starting and before the opening of an exhaustvalve.

It is preferable that a deviation between the difference in the controlparameter calculated previously and the difference in the controlparameter calculated at this time is determined on a predeterminedcondition and a control quantity for correcting an air-fuel ratio of themixture is calculated based upon the determined deviation.

The inventors have further focused attention on a relation between heatproduction in a cylinder and an air-fuel ratio of a mixture in thecylinder. That is, as shown in FIG. 2, in a case an air-fuel ratio of amixture is smaller than a stoichiometric air-fuel ratio (in a case of arich region), a change (rate) of heat production ∫dQ between the abovetwo predetermined points is extremely slight as compared to a leanregion. On the other hand, when an air-fuel ratio of the mixture entersinto a lean region thereof exceeding a stoichiometric air-fuel ratio,the heat production ∫dQ rapidly reduces generally in proportion to theair-fuel ratio. Therefore, when during the operating of an internalcombustion engine, a difference in the control parameter PV^(κ) betweentwo predetermined points, showing heat production ∫dQ is determined, aswell as a deviation in the difference between the previous calculatingvalue and this time's calculating value in regard to the controlparameter PV^(κ) is determined and a control quantity for correcting anair-fuel ratio of a mixture, such as a correction value of a fuel supplyquantity is set so that the deviation is maintained in the vicinity of apredetermined value (within a predetermined range), it is possible toalways maintain the air-fuel ratio of the mixture in the cylinderaccurately in the vicinity of a stoichiometric air-fuel ratio.

Further, preferably a control quantity for correcting an air-fuel ratioof a mixture is calculated so that the difference in the above controlparameter becomes equal to a target value on a predetermined condition.

As seen from FIG. 2, when an air-fuel ratio of a mixture in a cylinderis larger than a stoichiometric air-fuel ratio (when the air-fuel ratiobecomes lean), the heat production ∫dQ between the two predeterminedpoints reduces to a rapidly changing point prior to flameout (a leanlimit) generally in proportion to the air-fuel ratio as the air-fuelratio increases. Accordingly, when a difference in control parameterPV^(κ) between two predetermined points, showing heat production ∫dQ isdetermined and further, a control quantity for correcting an air-fuelratio of a mixture, such as a correction value of a fuel supply quantityis set so that the difference is equal to a predetermined target value,it is possible to maintain the air-fuel ratio of the mixture in thecylinder accurately in the vicinity of a desired target value (a leanregion) larger than a stoichiometric air-fuel ratio.

The best mode for carrying out the present invention will be hereinafterexplained in detail with reference to the drawings.

FIG. 3 is a schematic construction view showing an internal combustionengine according to the present invention. An internal combustion engine1 shown in the same figure burns a mixture of fuel and air inside acombustion chamber 3 formed in a cylinder block 2 and reciprocates apiston 4 inside the combustion chamber 3 to produce power. The internalcombustion engine 1 is preferably constructed of a multi-cylinder engineand the internal combustion engine 1 in the present embodiment isconstructed of, for example, a four-cylinder engine.

An intake port of each combustion chamber 3 is respectively connected toan intake manifold 5 and an exhaust port of each combustion chamber 3 isrespectively connected to an exhaust manifold 6. In addition, an intakevalve Vi and an exhaust valve Ve are disposed for each chamber 3 in acylinder head of the internal combustion engine 1. Each intake valve Viopens/closes the associated intake port and each exhaust valve Veopens/closes the associated exhaust port. Each intake valve Vi and eachexhaust valve Ve are activated by, for example, a valve operatingmechanism (not shown) including a variable valve timing function.Further, the internal combustion engine 1 is provided with ignitionplugs 7 the number of which corresponds to the number of the cylindersand the ignition plug 7 is disposed in the cylinder head for exposure tothe associated combustion chamber 3.

The intake manifold 5 is, as shown in FIG. 3, connected to a surge tank8. An air supply line L1 is connected to the surge tank 8 and isconnected to an air inlet (not shown) via an air cleaner 9. A throttlevalve 10 (electronically controlled throttle valve in the presentembodiment) is incorporated in the halfway of the air supply line L1(between the surge tank 8 and the air cleaner 9). On the other hand, apre-catalyst device 11 a including a three-way catalyst and apost-catalyst device 11 b including NOx occlusion reduction catalystare, as shown in FIG. 3, connected to the exhaust manifold 6.

Further, the internal combustion engine 1 is provided with a pluralityof injectors 12, each of which is, as shown in FIG. 3, disposed in thecylinder head for exposure to the associated combustion chamber 3. Andeach piston 4 of the internal combustion engine 1 is constructed in adeep-dish top shape, and the upper face thereof is provided with aconcave portion 4 a. In addition, fuel such as gasoline is directlyinjected from each injector 12 toward the concave portion 4 a of thepiston 4 inside each combustion chamber 3 in a state air is aspired intoeach combustion chamber 3 in the internal combustion engine 1. As aresult, in the internal combustion engine 1, a layer formed of a mixtureof fuel and air is formed (stratified) in the vicinity of the ignitionplug 7 as separated from an air layer in the circumference of themixture layer, and therefore, it is possible to perform stablestratified combustion with an extremely lean mixture. It should be notedthat the internal combustion engine 1 of the present embodiment isexplained as what you called a direct injection engine, but not limitedthereto, may be applied to an internal combustion engine of an intakemanifold (intake port) injection type without mentioning.

Each ignition plug 7, the throttle valve 10, each injector 12, the valveoperating mechanism and the like as described above are electricallyconnected to an ECU 20 which acts as a control apparatus of the internalcombustion engine 1. The ECU 20 includes a CPU, a ROM, a RAM, an inputand an output port, a memory apparatus and the like (any of them is notshown). Various types of sensors including a crank angle sensor 14 ofthe internal combustion engine 1 are, as shown in FIG. 3, connectedelectrically to the ECU 20. The ECU 20 uses various types of maps storedin the memory apparatus and also controls the ignition plugs 7, thethrottle valve 10, the injectors 12, the valve operating mechanism andthe like for a desired output based upon detection values of the varioustypes of sensors or the like.

In addition, the internal combustion engine 1 includes in-cylinderpressure sensors 15 (in-cylinder pressure detecting means) the number ofwhich corresponds to the number of the cylinders, each provided with asemiconductor element, a piezoelectric element, a fiber optical sensingelement and the like. Each in-cylinder pressure sensor 15 is disposed inthe cylinder head in such a way that the pressure-receiving face thereofis exposed to the associated combustion chamber 3 and is electricallyconnected to the ECU 20. Each in-cylinder pressure sensor 15 detects anin-cylinder pressure in the associated combustion chamber 3 to supply asignal showing the detection value to the ECU 20.

Next, operations of the internal combustion engine 1 will be explainedwith reference to FIG. 4.

When the internal combustion engine 1 is started and thereafter, istransferred from an idling state to an idling-off state, as shown inFIG. 4, the ECU 20 determines a target torque of the internal combustionengine 1 based upon a signal from a position sensor (not shown) for anaccelerator pedal or the like and sets an intake air quantity (theopening of the throttle valve 10) and a fuel injection quantity (fuelinjection time) from each injector 12 in accordance with the targettorque by using a map or the like in advance prepared (step S10).Further, at step S12, the ECU 20 sets the opening of the throttle valve10 to the opening thereof set at step S10, as well as injects, forexample, a quantity of fuel set during an intake stroke of the engine atstep S10 from each injector 12.

In addition, the ECU 20 monitors a crank angle of the internalcombustion engine 1 based upon a signal from the crank angle sensor 14.And the ECU 20, after each intake valve Vi opens and at the same timewhen the crank angle becomes first timing (the timing when the crankangle becomes θ1) set before ignition of each ignition plug 7,determines an in-cylinder pressure P (θ1) in each combustion chamber 3at the time when the crank angle becomes θ1, based upon a signal fromthe in-cylinder pressure sensor 15. Further, the ECU 20 calculates acontrol parameter P (θ1)·V^(κ) (θ1) in each combustion chamber 3 whichis a product of the determined in-cylinder pressure P (θ1) and a valueobtained by exponentiating an in-cylinder volume V (θ1) at the timing ofdetecting the in-cylinder pressure P (θ1), i.e. at the time the crankangle becomes (θ1) with a ratio κ (κ=1.32 in the present embodiment) ofspecific heat, and stores the calculated control parameter P (θ1)·V^(κ)(θ1) in a predetermined region of the RAM (step S14).

It is preferable that the first timing is set as the timing sufficientlyearlier prior to the time (ignition time) when combustion starts in eachcombustion chamber 3. In the present embodiment, the first timing is setas, for example, the timing when the crank angle shown in the signalfrom the crank angle sensor 14 becomes −60° (θ1=−60°, i.e. 60° before atop dead center). In addition, a value of V^(κ) (θ1) (a value of V^(κ)(−60°) in the present embodiment) is in advance calculated and is storedin the memory apparatus.

The ECU 20, after the processing of step S14, determines an in-cylinderpressure of P (θ2) in each combustion chamber 3 at the time when thecrank angle becomes θ2, based upon a signal from the in-cylinderpressure sensor 15 at a second timing (the timing when the crank anglebecomes θ2) set after ignition of each ignition plug 7, as well asbefore the opening of each exhaust valve Ve. Further, the ECU 20calculates a control parameter P (θ2)·V^(κ) (θ2) in each combustionchamber 3 which is a product of the determined in-cylinder pressure P(θ2) and a value obtained by exponentiating an in-cylinder volume V (θ2)at the timing of detecting the in-cylinder pressure P (θ2), i.e. at thetime the crank angle becomes (θ2) with a ratio κ (κ=1.32 in the presentembodiment) of specific heat, and stores the calculated controlparameter P (θ2) V^(κ) (θ2) in a predetermined region of the RAM (stepS16). It is preferable that the second timing is set as the timing whencombustion of a mixture in the combustion chamber 3 is substantiallycompleted. In the present embodiment, the second timing is set as, forexample, the timing when the crank angle shown in the signal from thecrank angle sensor 14 becomes 90° (θ1=90°, i.e. 90° after a top deadcenter). In addition, a value of V^(κ) (θ2) (a value of V^(κ) (90°) inthe present embodiment) is in advance calculated and then is stored inthe memory apparatus.

As described above, when the control parameter P (θ1)·V^(κ) (θ1) and P(θ2)·V^(κ) (θ2) is determined, the ECU 20 calculates a difference in thecontrol parameter PV^(κ) between the first and the second timing in eachcombustion chamber 3 as ΔV^(κ)=P(θ2)·V^(κ)(θ2)−P(θ1)·V^(κ)(θ1), andstores the calculated difference in a predetermined memory region of theRAM (step S18). This difference ΔPV^(κ), as described above, shows heatproduction ∫dQ in each combustion chamber 3 between the second timingand the first timing (the two predetermined points), i.e. a heatquantity generated in the combustion chamber 3 during the period fromthe first timing to the second timing. When the difference ΔPV^(κ) ofthe control parameter PV^(κ) is determined in each combustion chamber 3,the ECU 20 calculates an average value Qest (=Qestnew) of the differenceΔPV^(κ) of the control parameter PV^(κ) for every combustion chamber 3and stores the average value in a predetermined memory region of the RAM(step S20). Averaging thus the difference ΔPV^(κ) for every combustionchamber 3 allows the effect due to combustion variations between thecombustion chambers 3 on the subsequent processing to be alleviated.

The average value Qest of the difference ΔPV^(κ) in the controlparameter PV^(κ) properly reflecting the heat production between thefirst timing and the second timing is simply and quickly calculated bythe processing from step S14 to step S20 as described above. This causessignificant reduction of calculation loads in the ECU 20 as compared toa case of calculating heat production in each combustion chamber 3 byperforming the integral processing of the in-cylinder pressure for eachminute unit crank angle.

When the processing at step S20 is completed, the ECU 20 determines inwhich operational mode the internal combustion engine 1 should beoperated at this stage (step S22). The internal combustion engine 1according to the present embodiment can be operated at any one of astoichiometric operational mode in which an air-fuel ratio of a mixtureof fuel and air in each combustion chamber 3 is set to a stoichiometricair-fuel ratio (fuel to air=1 to 14.7) and a lean operational mode inwhich an air-fuel ratio of a mixture of fuel and air in each combustionchamber 3 is set to a desired target air-fuel ratio larger than astoichiometrical air-fuel ratio. And at step S22, the ECU 20 determineswhether or not a stoichiometric operational mode is executed basedparameters such as rotational speeds, loads, throttle openings, anddepressing acceleration of an accelerator pedal.

When at step S22, it is determined that the stoichiometric operationalmode should be executed, the ECU 20 calculates a deviation ΔQ between anaverage value Qestnew of the difference ΔPV^(κ) of the control parameterPV^(κ) calculated at step S20 following this time's ignition in eachcombustion chamber 3 and an average value Qestold of the differenceΔPV^(κ) of the control parameter PV^(κ) calculated at step S20 followingthe previous ignition in each combustion chamber 3 as ΔQ=Qestnew−Qestold(step S24).

As herein explained in association with FIG. 2, when an air-fuel ratioof a mixture is small than a stoichiometric air-fuel ratio (a case of arich region), a change (rate) of heat production ∫dQ between twopredetermined points is extremely small as compared to a lean region. Onthe other hand, when an air-fuel ratio of a mixture in the combustionchamber 3 enters into a lean region exceeding a stoichiometric air-fuelratio, the heat production ∫dQ rapidly reduces generally in proportionto the air-fuel ratio. Accordingly, if the deviation ΔQ (inclination ofthe heat production in FIG. 2) between this time's calculation valueQestnew and the previous calculation value Qestold of the differenceΔPV^(κ) in the control parameter PV^(κ) between the two predeterminedpoints showing the heat production ∫dQ is maintained in the vicinity ofa predetermined value (within a predetermined range), the heatproduction ∫dQ between the two predetermined points is substantiallyconstant after and before one time's ignition and the air-fuel ratio ofthe mixture is also substantially constant.

Therefore, when the ECU 20 determines the deviation ΔQ at step S24, theECU 20 compares the deviation ΔQ with a predetermined threshold value a(negative predetermined value), thus determining whether or not anair-fuel ratio of the mixture in each combustion chamber 3 is largerthan a stoichiometric air-fuel ratio (is lean)(step S26). In a case theECU 20 determines that the mixture in each combustion chamber 3 is lean(the deviation ΔQ is less than the threshold value a) at step S26, theECU 20 sets a correction value of a fuel injection quantity so that thefuel injection quantity from each injector 12 is slightly increased(step S28). Accordingly, even if the air-fuel ratio of the mixture ineach combustion chamber 3 during the stoichiometric operational mode islarger than the stoichiometric air-fuel ratio, it is possible to makethe air-fuel ratio of the mixture in each combustion chamber 3 be closeto the stoichiometric air-fuel ratio by making the mixture in eachcombustion chamber 3 be rich.

In addition, in a case at step S26, the ECU 20 determines that themixture in each combustion chamber 3 does not become lean, the air-fuelration of the mixture in each combustion chamber 3 is assumed to besmaller than the stoichiometric air-fuel ratio (to be rich) to set acorrection value of a fuel injection quantity so that the fuel injectionquantity from each injector 12 is slightly reduced as needed (step S30).Accordingly, even if the air-fuel ratio of the mixture in eachcombustion chamber 3 during the stoichiometric operational mode issmaller than the stoichiometric air-fuel ratio, it is possible to makethe air-fuel ratio of the mixture in each combustion chamber 3 be closeto the stoichiometric air-fuel ratio by making the mixture in eachcombustion chamber 3 be lean. It should be noted that in the presentembodiment, the correction value of the fuel injection quantity set ateach of steps S28 and S30 is a predetermined constant quantity and maybe calculated in accordance with a difference between the deviation ΔQand the threshold value.

On the other hand, in a case it is determined that at step S22, thestoichiometric operational mode should not be executed, that is, thelean operational mode should be executed, the ECU 20 reads out a targetvalue Qt of heat production in accordance with a target air-fuel ratioin the lean operational mode from the memory apparatus, as well ascalculates a deviation e between the average value Qest of thedifference ΔPV^(κ) in the control parameter PV^(κ) determined at stepS20 and a target value Qt as e=Qest−Qt (step S32). In addition, the ECU20 calculates (sets) a correction value of a fuel injection quantity sothat the deviation e determined at step S32 is made to be zero by usinga map in advance prepared or a predetermined function expression (stepS34).

As explained herein in association with FIG. 2, when an air-fuel ratioof the mixture in each combustion chamber 3 becomes larger than astoichiometric air-fuel ratio (becomes lean), the heat production ∫ dQbetween the two predetermined points reduces generally in proportion tothe air-fuel ratio to a rapid changing point (lean limit point) prior toflameout as the air-fuel ratio increases. Accordingly, in the region(lean region) where the air-fuel ratio of the mixture is larger than astoichiometric air fuel ratio, the deviation e between the average valueQest of the difference ΔPV^(κ) in the control parameter PV^(κ) betweenthe two predetermined points determined at step S20 and the target valueQt is made to be zero, thereby making it possible to maintain anair-fuel ration of the mixture in each combustion chamber 3 to be adesired (lean) target air-fuel ratio larger than a stoichiometricair-fuel ratio. That is, in the internal combustion engine 1, a feedbackcontrol is performed for making the average value Qest of the differenceΔPV^(κ) in the control parameter PV^(κ) be close to the target value Qtat a lean operational mode. Thereby, in the internal combustion engine1, it is possible to make the mixture in each combustion chamber 3 be aslean as possible to the vicinity of the lean limit region in FIG. 2,i.e. it is possible to carry out a lean limit operation by properlysetting the target value Qt of the heat production therein.

As described above, the ECU 20 sets a correction value of a fuelinjection quantity at step S28 or S30 in the event of a stoichiometricoperational mode, and a correction value of a fuel injection quantity atstep S34 in the event of a lean operational mode. And the ECU 20 goesback to step S10, wherein a fuel injection quantity (fuel injectiontime) from each injector 12 is set considering (adding/subtracting) thecorrection value of the fuel injection quantity set at step S28, S30 orS34, as well as the opening of the throttle valve 10 is set torepeatedly execute the processing after the step S12. Such a series ofthe processing is repeated by the ECU 20 during the period when anidling-off state continues.

As explained above, since according to the internal combustion engine 1,in the event of a stoichiometric operational mode, an air-fuel ratio ofa mixture in each combustion chamber 3 is set accurately in the vicinityof a stoichiometric air-fuel ratio by using a difference ΔPV^(κ) in thecontrol parameter PV^(κ) roperly reflecting heat production between thetwo predetermined points, the region where a ratio λ of a supply airquantity to a astoichiometric air-fuel ratio is equal to 1 (λ=1) can beexpanded. In addition, according to the internal combustion engine 1, inthe event of a lean operational mode, an air-fuel ratio of a mixture ineach combustion chamber 3 is set accurately to a predetermined targetair-fuel ratio larger than a stoichiometric air-fuel ratio by using adifference ΔPV^(κ) in control parameter PV^(κ) properly reflecting heatproduction between the two predetermined points.

In this way, an air-fuel ratio control in the internal combustion engine1 is performed by using a difference ΔPV^(κ) in control parameter PV^(κ)properly reflecting heat production between two predetermined points andthereby, it is possible to resolve problems with what you called adetection delay or a transport lag recognized in a case an in-cylinderair-fuel ratio is controlled (feedback-controlled) based upon, forexample, an exhaust air-fuel ratio detected in an exhaust system for aninternal combustion engine, significantly improving response andaccuracy in an air-fuel ratio control. In addition, as described above,since a highly accurate air-fuel ratio control is performed by using adifference ΔPV^(κ) in control parameter PV^(κ), it is possible to omitan air-fuel ratio sensor for detecting an exhaust air-fuel ratio, anair-flow meter for detecting an intake air quantity and the like, whichare absolutely necessary for the conventional air-fuel ratio control,leading to enabling the construction of the internal combustion engine 1at low costs. In addition, realization of the highly accurate air-fuelratio causes purification loads on a catalyst to be reduced, therebyenabling downsizing of a catalyst apparatus.

It should be noted that a control quantity for correcting an air-fuelratio of a mixture in each combustion chamber 3 is not limited to acorrection value of a fuel injection quantity, but may be a correctionvalue of a throttle valve, a correction value of an exhaust gasrecirculation quantity in an internal combustion engine provided with anexhaust gas recirculation system or a combination thereof. That is, inthe processing at steps S28, S30 and S34, when at least any one ofcorrection values of a fuel injection quantity, an opening of a throttlevalve, an exhaust gas recirculation quantity, and the like is set, itallows correcting an air-fuel ratio of a mixture in each combustionchamber 3. Further, the present invention can be applied not only to agasoline engine but also to a diesel engine without mentioning.

In addition, if a map or the like defining a relation between a valueQest showing actual heat production and an air-fuel ratio (actualair-fuel ratio) of a mixture in each combustion chamber 3 is in advanceprepared on a basis that the air-fuel ratio of the mixture in eachcombustion chamber 3 in a lean region is generally in proportion to heatproduction Q (refer to FIG. 2), the actual air-fuel ratio in accordancewith the Qest can be calculated from the map or the like. Accordingly,at steps S32 and S34 in FIG. 4, the actual air-fuel ratio in accordancewith the Qest showing the actual heat production is calculated, as wellas a deviation between the calculated air-fuel ratio and a targetair-fuel ratio set in accordance with an engine rotational speed and anengine load is determined, and a control quantity (for example, thecorrection of the fuel injection quantity) for correcting the air-fuelratio of the mixture in each combustion chamber 3 may be set inaccordance with the determined deviation. When the control parameterPV^(κ) is thus used, it is possible to accurately detect the air-fuelratio in the internal combustion engine 1.

INDUSTRIAL APPLICABILITY

The present invention is useful in a control apparatus and a controlmethod for an internal combustion engine with practicability which issimply able to perform a highly accurate engine control at low loads.

1. A control apparatus for an internal combustion engine which generatespower by burning a mixture of fuel and air in a cylinder thereof,comprising: in-cylinder pressure detecting means; calculating means forcalculating a control parameter based upon the in-cylinder pressuredetected by the in-cylinder pressure detecting means and an in-cylindervolume at a timing of detecting the in-cylinder pressure; and controlmeans for setting a predetermined control quantity based upon thecontrol parameter calculated by the calculating means.
 2. The controlapparatus for the internal combustion engine according to claim 1,wherein: the control parameter includes a product of the in-cylinderpressure detected by the in-cylinder pressure detecting means and avalue obtained by exponentiating the in-cylinder volume at the timing ofdetecting the in-cylinder pressure with a predetermined index.
 3. Thecontrol apparatus for the internal combustion engine according to claim2, wherein: the calculating means calculates the control parameters attwo predetermined points; and the control means sets a predeterminedcontrol quantity based upon a difference in the control parameterbetween the two predetermined points.
 4. The control apparatus for theinternal combustion engine according to claim 3, wherein: one of the twopredetermined points is set as a point after the opening of an intakevalve and before the combustion starting of the mixture; and the otheris set as a point after the combustion starting and before the openingof an exhaust valve.
 5. The control apparatus for the internalcombustion engine according to claim 3, wherein: the control meansdetermines a deviation between the difference in the control parametercalculated previously and the difference in the control parametercalculated at this time on a predetermined condition and sets a controlquantity for correcting an air-fuel ratio of the mixture based upon thedetermined deviation.
 6. The control apparatus for the internalcombustion engine according to claim 3, wherein: The control means setsa control quantity for correcting an air-fuel ratio of the mixture sothat the difference in the control parameter is equal to a target valueon a predetermined condition.
 7. A control method for an internalcombustion engine which generates power by burning a mixture of fuel andair, comprising the steps of: (a) detecting an in-cylinder pressure; (b)calculating a control parameter based upon the in-cylinder pressuredetected in the step (a) and an in-cylinder volume at a timing ofdetecting the in-cylinder pressure; and (c) setting a predeterminedcontrol quantity based upon the control parameter calculated in the step(b).
 8. The control method for the internal combustion engine accordingto claim 7, wherein: the control parameter includes a product of thein-cylinder pressure detected in the step (a) and a value obtained byexponentiating the in-cylinder volume at the timing of detecting thein-cylinder pressure with a predetermined index.
 9. The control methodfor the internal combustion engine according to claim 8, wherein: in thestep (b), the control parameters are calculated at two predeterminedpoints; and in the step (c), a predetermined control quantity is setbased upon a difference in the control parameter between the twopredetermined points.
 10. The control method for the internal combustionengine according to claim 9, wherein: one of the two predeterminedpoints is set as a point after the opening of an intake valve and beforethe combustion starting of the mixture and the other is set as a pointafter the combustion starting and before the opening of an exhaustvalve.
 11. The control method for the internal combustion engineaccording to claim 9, wherein: the step (c) includes the steps of:determining a deviation between the difference in the control parametercalculated previously and the difference in the control parametercalculated at this time on a predetermined condition; and setting acontrol quantity for correcting an air-fuel ratio of the mixture basedupon the determined deviation.
 12. The control method for the internalcombustion engine according to claim 9, wherein: the step (c) includesthe step of: setting a control quantity for correcting an air-fuel ratioof the mixture so that the difference in the control parameter is equalto a target value on a predetermined condition.